The present invention relates generally to valves and more particularly to variable orifice dual gate valve construction especially designed to control flow of viscous liquids and for other mixtures as solid, or semisolid bearing fluids, such as pulverized fuel flow for coal burning industrial furnaces.
Gate valves manufactured of materials which are resistant to wear and erosion are commonly used to feed pulverized coal and air mixtures to industrial furnaces as fuel. The mixture is normally transported at a rate of 7,500 feet per minute and at a temperature of 120.degree. to 180.degree. F. The adjustment of the valve orifice is generally regulated by a single valve gate or dual valve gates which are operated from a single handle, but with dual actuators for the respective valve gate. Such dual actuator systems are expensive to manufacture and assemble and are prone to misalignment and binding. In addition, it is difficult to provide an accurate indicator for such valves to indicate a percentage of open area of the orifice of the valve in operation.
It is a principal object of the present invention to eliminate these aforementioned disadvantages of the prior art dual gate valves.